1. Field of the Invention
The present invention relates to solenoid operated pump-line-nozzle fuel injections systems for internal combustion engines. In particular, to such fuel injection systems in which an inline injection pump utilizes a solenoid-operated control for regulating injection timing and the quantity of fuel injected.
2. Description of Related Art
Inline injection pumps and pump-line-nozzle fuel injections systems using such pumps are old and well known. A discussion of several examples of such pumps and systems, and the efforts taken to improve their construction so that the increasing demands for low exhaust emissions can be met, can be found, for example, in SAE publication no. SP-703, Recent Developments in Electronic Engine Control & Fuel Injection Management, paper Nos. 870433, 870434 and 870436, pages 37-42, 43-51 and 65-77 published February, 1987. Inline pumps have a separate pumping cylinder for supplying fuel to each injection nozzle of the injection system, to which it is connected by a fuel line (hence, the name pump-line-nozzle injection system), a respective injection nozzle being provided for each engine cylinder. While inline pumps, such as those described in the papers cited above, are able to independently control injection timing and injection quantity, none of the known inline pumps produces individual cylinder control of both timing and fuel quantity on an infinitely adjustable basis; that is, typically such pumps having a control rack which adjusts all pumping cylinders in the same manner at the same time, and frequently using a step-wise adjusting driver.
Another type of pump used in pump-line-nozzle systems is a distributor pump. Examples of such pumps can be found in U.K. Patent Nos. 442,839 and 1,306,422 as well as U.S. Pat. Nos. 3,035,523 and 4,502,445, and a system and component description of both inline and distributor pumps can be found at page 24 of the above-cited SAE publication SP-703 in paper no. 870432 as well. In distributor pumps, only a single pumping cylinder is provided and a rotary distributor determines which injection nozzle will receive a specific dose of fuel. Inherently, such pumps cannot provide individual cylinder control since they lack individual pumping cylinders to control; however, as indicated, e.g., in U.S. Pat. Nos. 2,947,257 and 2,950,709, such distributor pumps can be constructed as multicylinder pumps as well (but in such a case they essentially become inline pumps, with a rack, cam or other single regulating mechanism being used to control "the whole of the injectors" and to insure that fuel delivery "is the same for all the cylinders"), so that individual cylinder control is still not obtained.
Another type of fuel injection system, which is fundamentally different from pump-line-nozzle systems, is the unit injector fuel injection system. In such a system, a positive displacement pump is used to supply fuel at low pressure, typically at constant pressure of e.g., 30 psi, to a respective unit fuel injector associated with each engine cylinder. The unit injectors, themselves, regulate the timing and metering of the fuel into the respective engine cylinder and also develop the high pressure, e.g., at least 15,000 psi at which the fuel needs to be injected into the engine cycle if the requirements for increased fuel economy and decreased emissions are to be achieved.
Solenoid operated fuel injectors of the unit injector type having characteristics of the type sought to be obtained with the inline pump of the pump-line-nozzle injector system of the present invention have been in use for some time, and an example of such an injector can be found in commonly-owned U.S. Pat. No. 4,531,672 to Smith. In this type of injector, a timing chamber is defined between a pair of plungers that are reciprocatingly displaceable within the bore of the body of the injector and a metering chamber is formed in the bore below the lower of the two plungers. A supply rail in the engine delivers a low pressure supply of fuel to the injector body. To control this supply of fuel, a solenoid valve is disposed in the flow path between the fuel supply rail and the injector bore and the plungers block and unblock respective ports leading from injector body fuel supply circuit into the timing and metering chambers.
During the operation of such an injector, the port to the timing chamber is opened during retraction of the plungers to allow fuel to enter the timing chamber. During the injector downstroke, the timing port is closed by the upper plunger, and then, the metering port is opened to direct the supply of fuel into the metering chamber. During the entire time, from the start of the timing period through the end of the metering period, the solenoid valve remains open.
In an existing unit injector design, sold by the Cummins Engine Co. under the CELECT trademark, shown in FIGS. 1-3, improved performance is achieved. In this existing unit fuel injector 1, as shown in FIG. 1, initially, during the retraction stroke, with the solenoid valve 3 closed, the metering plunger 5 and the timing plunger 7 rise together, and fuel under rail pressure is metered into the metering chamber 9. When the proper quantity of fuel has been metered, the solenoid valve 3 is opened (FIG. 2), allowing fuel to flow into the timing chamber 11, causing the pressure at the top and bottom of the metering plunger to be equalized, thereby stopping movement of the metering plunger 5 while the timing plunger 7 continues to rise, and the timing chamber 11 to fill, as the retraction stroke is completed.
During the downstroke, prior to the time at which injection is to commence, as shown in FIG. 3, the solenoid valve 3 remains open and fuel is forced back out of the timing chamber 11, through the solenoid valve 3 into supply circuit. A relief valve assembly 15 is provided to vent high pressure spikes from the rail side of the injector 1 to the drain side thereof (enlarged detail of FIG. 3). More specifically, the relief valve assembly 15 comprises a valve member 15a which is urged against a relief port 15b by a coil spring 15c which is disposed in a barrel member 17, the upper surface of which forms the bottom wall of the metering chamber 9 and which contains channels through which fuel flows between the fuel inlet port and the metering chamber and from the metering chamber to a drain passage 21. When the pressure of the backflowing timing fluid exceeds that of spring 15c, the valve member 15a unblocks relief port 15b, thereby opening a path from the fuel supply circuit to drain passage 21. At the end of the injection phase, when the solenoid 3 is closed, the top edge of the metering plunger 5 passes below at least one timing fluid spill port 23, thereby evacuating the timing chamber 11 via the drain passage 21. Additionally, passages 5a in the metering plunger 5 are brought into communication with at least one spill port 25 by which a small quantity of fuel is spilled to the fuel supply circuit. Then, the described cycle of events is repeated.
However, while unit fuel injector fuel injection systems are available by which the amount of fuel injected and timing of its injection can be independently and infinitely adjusted on a individual cylinder and cycle-to-cycle basis, using a relatively simple, single solenoid control for each injector, unit injectors, due to increased tasks associated therewith in comparison to the injection nozzle of a pump-line-nozzle injection system, is relatively large in comparison to the injection nozzle of pump-line-nozzle injection systems. As a result, the use of unit fuel injector system has been confined to large, heavy duty engines since insufficient space exists in the engine valve area of smaller engines to accommodate unit fuel injectors. Thus, there still is a need for further improvements to pump-line-nozzle fuel injector systems of the: type to which this invention is directed, in order to provide the degrees of precision control needed to meet the competing demands for both increased fuel economy and decreased engine exhaust emissions.